This invention relates generally to antiseptic teat dips, and more particularly to a teat dip including iodine as an antimicrobial agent and propylene glycol as a primary carrier for the iodine.
Mastitis is a major world-wide problem for operations involving dairy animals, such as cows and goats. It is estimated that mastitis results in a per annum production loss to dairy farmers in the United States alone of between two and three billion dollars. Therefore, control of mastitis is of great concern to those in the dairy industry.
Mastitis is caused by infections of the mammary, or milk-producing glands by a broad spectrum of pathogenic microorganisms, such as Staphylococcus aureus, Streptococcus agalactiae, Escherichia coli, Mycoplasma bovis, and Candida albicans. In particular, when the milk-producing glands and surrounding tissue in the udder become infected, the tissue becomes inflamed with cellular infiltrates and associated toxins. The cellular infiltrates and associated toxins can cause a dramatic reduction in the quality of milk produced by an infected dairy animal. The quantity of milk produced is also usually affected, sometimes resulting in a total stoppage of production.
Occasionally, an infection will spread systemically to other organ and tissue sites via the blood or lymphatic systems. The spreading infection can, in extreme cases, seriously debilitate or kill the infected animal.
One effective way to control or prevent mastitis is by killing the pathogenic organisms which might otherwise infect the teat and udder tissues before the organism enters the tissues. This is accomplished by disinfecting the teats of the dairy animal both before and after milking with a topical antiseptic composition commonly known as a “teat dip.” Such compositions kill or reduce the number of microorganisms on the teat surface before the microorganisms can migrate or be propelled during milking into the teat canal, or enter the teat via lesions or injuries. In fact, more than 50% of new udder infections can be prevented by disinfecting teats with an effective product immediately before or after every milking.
In addition to disinfecting teats immediately after milking, use of good milking and environmental management procedures, use of properly functioning milking equipment, and early identification and treatment or management of mastitis cases are part of an effective mastitis control plan. However, post-milking teat disinfection is the single most effective practice to reduce the rate of intramammary infection by contagious pathogens, such as Staph. aureus. In addition, a degree of control over environmental pathogens, such as E. coli, is exerted.
The present invention relates to an antiseptic teat dip comprising iodine as an antimicrobial agent. Current antiseptic teat dips containing iodine are iodophors. For the purposes of this invention, an iodophor is defined as a complex of iodine and a carrier molecule, such as non-ionic ethoxylated surfactants, cationic surfactants, poloxamers and polyvinylpyrrolidone (PVP). The complexed form of iodine, or iodophor, is not itself germicidal. Instead, it is I2, or free iodine, that has the germicidal properties. Higher levels of free iodine in any given solution tend to allow for a quicker and more effective kill of microorganisms. In solution, the complexed iodine is in equilibrium with free iodine. As the free iodine is depleted, more free iodine is released from its complex to maintain the equilibrium.
The equilibrium level of free iodine in iodophor-based teat dip compositions depends on many factors, including the concentration of available iodine and the type of complex used. “Available iodine” is the total amount of complexed and free iodine in the system that can be measured by titration with sodium thiosulfate. While normally a higher concentration of iodophor (higher available iodine) in the composition results in a higher concentration of free iodine being released, this is not always the case. For example, an iodophor of iodine complexed with PVP produces higher equilibrium levels of free iodine as it is diluted. As a result, iodine-PVP compositions having an available iodine concentration of 1.0% are less germicidal over short exposure periods than iodine-PVP compositions having an available iodine concentration of between 0.01% and 0.1%. In the PVP-iodine iodophors, the iodine is in the form of tri-iodide (I3). Upon dilution, the fin, PVP-iodine complex is weakened, thereby releasing free iodine and increasing the equilibrium level of free iodine. This is thought to be a result of the dispersion of micellular aggregates.
When concentrated iodine-PVP compositions are diluted, more free iodine as a percentage of available iodine is released. For example, in an iodine-PVP composition diluted to a concentration of 0.001% available iodine (10 ppm), virtually all of the iodine is present as free iodine. We have found that the maxium amount of free iodine present in an iodine-PVP composition occurs when the available iodine is at a concentration of approximately 0.01% (100 ppm). En this system, approximately 30%, or 30 ppm of the available iodine is present as free iodine.
Other iodophors operate differently than iodine-PVP iodophors. We have found that for non-ionic type complexes, compositions having higher concentrations of available iodine contain more free iodine. Thus, the chemistry of iodophors and iodine is complex. In addition, there are other factors besides the type of iodophor complex used that may affect the amount of free iodine in a given composition, such as pH, temperature, levels of iodides and iodates, emollient type and concentration, and dilution with water.
We have found that higher levels of free iodine can increase the speed of germicidal activity, especially for certain types of iodine complexes. Speed of germicidal activity is important for teat dip formulations, because the formulation may be on the animal's teats for only a limited period of time before it is removed. It is desirable for a teat dip composition to have a free iodine level of at least 5-10 ppm of free iodine in order to generate an acceptable speed of germicidal activity.
As stated above, in an iodophor composition, the free iodine concentration is in equilibrium with the iodine complex. Thus, as the free iodine is depleted, more is produced from the remaining iodine complex. Because iodine is a highly reactive oxidizing agent, it will react with a wide variety of molecules. In addition, elemental iodine in solution is quite volatile. As a result, the available iodine may be depleted prior to completion of the antiseptic process. This is a problem with iodophor teat dips. Also, dilute preparations of iodophors are unstable over time, because of the relatively high levels of free iodine present at equilibrium. These two characteristics result in the unsuitability of dilute iodophor preparations as teat dips. Conventional concentrated iodophor teat dip compositions are also unsuitable because of irritation problems in the animals being treated resulting from the high iodine levels in the composition.
Therefore, formulating an effective teat dip, even under laboratory conditions, is challenging. This challenge is multiplied by the environment in which these compositions are actually used. Not only are the animal's teats physically stressed due to the repeated handling and milking, but the teats are also chemically stressed due to the repeated use of chemical teat dips and udder washes. In addition, the teats are subjected to environmental stress, such as the cold, windy and dry conditions in the winter and the sun exposure in the summer. For example, water-based teat dips can freeze on the teat skin after application in cold, windy conditions, contributing to teat chapping or even frostbite. Such damage to the teats promotes colonization of microorganisms, which, in turn leads to a higher incidence of mastitis. Thus, many in the dairy industry do not use teat dip on their animals in such conditions. Moreover, on a daily basis, the teats are subjected to potentially high levels of pathogenic microorganisms from a variety of sources including the milking machines, soil, bedding, water, other animals, and the air. As stated above, teat skin that is damaged and/or stressed is more susceptible to colonization with mastitic microorganisms.
Therefore, iodine teat dip compositions have been developed that contain component at sufficiently high levels to effectively protect, heal and/or condition the teat skin. For example, U.S. Pat. No. 4,012,504 discloses a teat dip composition made by dissolving up to 7% by weight crystalline iodine in an animal or vegetable oil, specifically mineral oil, at an elevated temperature, and allowing the composition to cool. The '504 patent further discloses that preferably from about 0.2% to about 2% by weight iodine should be used. Theoretically, the amount of free iodine in such a composition should be quite high, limited only by the solubility of the iodine in mineral oil. This is in fact the case, as shown in Table 1, which lists the amount of free iodine resulting from various iodophor compositions, as well as the amount of free iodine resulting from an iodine/mineral oil and an iodine/water composition. The amount of free iodine for each composition was determined by dialysis, at 24 hours after preparation and after 216 hours for iodine/mineral oil and iodine/water.
The dialysis procedure was as follows:
100 ml of acidified water (water adjusted to a pH of 45 with phosphonic acid) was measured into a glass wide-mouth container. 50 ml of the sample to be analyzed was then placed in a polyethylene bag, and the bag was placed in the acidified water, with the sample portion submerged. The container was then allowed to stand for 16-24 hours at ambient temperature to reach equilibrium. 9 ml of acidified water was then removed from transferred to a cuvette and its absorbance was measured at 353 nm on a spectrophotometer against an acidified water reference sample. A standard iodine solution was then prepared by dissolving 0.30 g of iodine in 1000 ml of deionized water. The percentage of available or titratable iodine was determined using a standard 0.01N sodium thiosulfate solution titratration. 1 ml of the standard iodine solution was then mixed with 10 ml of 1M KI and 89 ml of acidified water, and the absorbance of this solution at 353 nm was determined. The amount of free iodine in the sample was then calculated using the following equation:IF=A1×(Vs/Va)×(Is/A2)
where IF is ppm of free iodine in sample; A1 is the net absorbance of sample; Vs is total sample volume; Va is the volume of additional water in sample; Is is ppm of free iodine in standard solution; A2 is the net absorbance of standard solution.
TABLE 1  Free Iodine Determination - Dialysis MethodCOMPOSITIONFREE IODINE (PPM)After 24 Hours 0.7% iodine-Mineral oil1113.6 0.7% iodine-water63.3 0.1% non-ionic iodophor2.9 0.25% non-ionic iodophor3.2 0.5% non-ionic iodophors (average)15.2 1.0% non-ionic iodophors (average)17.8 1.0% non-ionic iodophors w/10% glycerin10.1(average)0.036% PVP iodophor13.80.055% PVP iodophor12.20.103% PVP iodophor9.40.516% PVP iodophor4.00.930% PVP iodophor2.8After 216 Hours 0.7% iodine-Mineral oil107.1 0.7% iodine-water10.61Percent iodine is the amount of available iodine in the composition. 
As can be seen in Table 1 and as stated above, iodine-PVP complexes show increased free iodine concentration as the amount of available iodine decreases, while the non-ionic ethoxylated iodophors show just the opposite—that free iodine increases with increasing available iodine concentration.
Although the composition of the '504 patent (iodine/mineral oil) has a high level of free iodine, it is not germicidally effective in the laboratory or in the field under actual use conditions. One explanation for the ineffectiveness of this composition might be that the hydrophobic nature of the mineral oil prevents much of the iodine from actually reaching the microorganisms to be killed.
In the '504 patent, mineral oil was used as the carrier, or solvent, for the iodine. Iodophors have also contained emollients and humectants in relatively small amounts in an attempt to condition teat skin. The prevailing view, however, is that the germicidal activity of teat dip compositions may be reduced if the concentration of emollients in the composition is greater than 10% to 12% by weight. Pankey et al., J. Dairy Sci., 67:1336 (1984). For example, as shown in Table 1, a non-ionic iodophor composition comprising 1.0% available iodine has 17.8 ppm free iodine, while the same composition having 10% glycerin added has only 10.1 ppm free iodine. The conclusion is that this and other iodine compositions maybe less stable when teat conditioners, such as emollients and humectants, are present.
Therefore, there is a need for an iodine-based teat dip composition that is effective as a germicide in short teat skin contact times, and also is a protecting and/or a healing agent for teat skin. There is also a need for an iodine-based teat dip composition that is stable over relatively long periods of time. There is a further need for an iodine-based teat dip composition that is highly efficacious, but is non-irritating in use. There is a yet another need for an iodine-based teat dip composition that can be used effectively to treat and/or prevent mastitis in a variety of weather conditions, and will not freeze in cold and windy weather. These needs are met by the teat dip composition of the present invention.